Today, let's look for the Tower of Babel. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.

The Tigris and Euphrates
Rivers flow down through Iraq to the Persian Gulf,
just North of Kuwait. Ancient Babylon sat on the
Euphrates. It was about 50 miles south of Baghdad,
which sits on the Tigris. The old nation of
Babylonia centered on those two cities and those
two rivers.

In the city of Aqar Quf, north of Babylon and West
of Baghdad, a huge clay structure rises 150 feet.
It's weathered and formless now. But it once formed
the base for a great temple in the sky. It was
built around 1400 BC. It's one of the best remains
of a structure called a ziggurat.

To understand ziggurats, we must understand the
soil along the Tigris and Euphrates. Those great
watercourses dump silt during flood season. The
silt constantly settles. Building on that substrate
is like building on quicksand.

Ancient engineers used a very modern technique to
solve the problem. They laid down alternating
layers -- first brick, then sandy soil laced with
reed matting. They formed huge terraces from these
layers. The bricks took the vertical load. The
tough matting kept the structure from slumping to
the side when it got wet. It was an ancient example
of what we call building with composite materials.

The Sumerians made the first ziggurats this way in
4000 BC -- before we had writing, or even the
wheel. Nebuchadnezzar built the last great ziggurat
in Babylon in 600 BC. Archaeologists locate some
twenty ziggurats in the region.

The excavation of Babylon is complete and clear.
The tower once rose from its center. We read the
inscription on an old slab, found near that spot.
It says,

I am Nebuchadnezzar, King of Babylon. I have paved
the Babel Street with slabs from Shadu for the
Procession of the great God Marduk.

Nebuchadnezzar's ziggurat rose 250 feet
above Babel street. Of course, that was after the
Genesis story of the Tower of Babel. But Babel Street
was also the site of older ziggurats, built and torn
down. Maybe one of them was the tower in Genesis.

We're told that the Tower of Babel had to fall
because it was pure pretension. It was neither art
nor worship. But many ancient ziggurats were much
more. They represented the origins of reinforced
concrete. They reflected the spirit of the great
works of civil engineering. And they -- far from
collapsing under the weight of pretension -- still
stand today.

I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.